Adenoviral-mediated transfer of Escherichia coli uracil phosphoribosyltransferase (UPRT) gene to modulate the sensitivity of the human colon cancer cells to 5-fluorouracil

Novel biomolecule lycopene-reduced graphene oxide-silver nanoparticle enhances apoptotic potential of trichostatin A in human ovarian cancer cells (SKOV3)

Background

Recently, there has been much interest in the field of nanomedicine to improve prevention, diagnosis, and treatment. Combination therapy seems to be most effective when two different molecules that work by different mechanisms are combined at low dose, thereby decreasing the possibility of drug resistance and occurrence of unbearable side effects. Based on this consideration, the study was designed to investigate the combination effect of reduced graphene oxide-silver nanoparticles (rGO-AgNPs) and trichostatin A (TSA) in human ovarian cancer cells (SKOV3).

Methods

The rGO-AgNPs were synthesized using a biomolecule called lycopene, and the resultant product was characterized by various analytical techniques. The combination effect of rGO-Ag and TSA was investigated in SKOV3 cells using various cellular assays such as cell viability, cytotoxicity, and immunofluorescence analysis.

Results

AgNPs were uniformly distributed on the surface of graphene sheet with an average size between 10 and 50 nm. rGO-Ag and TSA were found to inhibit cell viability in a dose-dependent manner. The combination of rGO-Ag and TSA at low concentration showed a significant effect on cell viability, and increased cytotoxicity by increasing the level of malondialdehyde and decreasing the level of glutathione, and also causing mitochondrial dysfunction. Furthermore, the combination of rGO-Ag and TSA had a more pronounced effect on DNA fragmentation and double-strand breaks, and eventually induced apoptosis.

Conclusion

This study is the first to report that the combination of rGO-Ag and TSA can cause potential cytotoxicity and also induce significantly greater cell death compared to either rGO-Ag alone or TSA alone in SKOV3 cells by various mechanisms including reactive oxygen species generation, mitochondrial dysfunction, and DNA damage. Therefore, this combination chemotherapy could be possibly used in advanced cancers that are not suitable for radiation therapy or surgical treatment and facilitate overcoming tumor resistance and disease progression.

Genetic Modification of Hepatocytes towards Hepatocyte Transplantation and Liver Tissue Engineering

Cell-based therapies, including liver tissue engineering following hepatocyte transplantation, have therapeutic potential for several types of liver diseases. Modifications in the methodology to manipulate the donor hepatocytes in a more simple and timely manner prior to transplantation would enhance the therapeutic efficacy of this procedure. Conventional approach for vector-mediated gene transduction to the isolated hepatocytes has been performed under primary culture conditions that routinely require several days to complete. In our study, we have established a clinically feasible approach that requires only 1 h of infection time with an adenoviral vector system that results in an extremely efficient transduction efficiency (>80%). To optimize transduction efficiency and sustain normal cellular function, we determined that the isolated hepatocytes should be maintained in UW solution as a suspension medium and infected with adenoviral vectors (Ad) for no more than 1 h at a MOI of 1. To establish if the isolated hepatocytes could be used as a source for cell-based therapies, we transplanted the Ad-transduced hepatocytes into the liver or under the kidney capsule. When the cells were transplanted into the liver, Ad-transduced hepatocytes cultured in suspension conditions were found to have a significantly higher survival rate (p < 0.01) than Ad-transduced hepatocytes cultured under standard conditions. We also confirmed that these Ad-transduced hepatocytes have ability to survive long term and were able to engineer a biologically active hepatic tissue under the kidney capsule. Finally, we obtained high level of transduction into canine, porcine, and human isolated hepatocytes in a suspension solution mixed with Ad. In conclusion, the present studies demonstrate that isolated hepatocytes could be genetically modified using Ad when kept in a suspension solution. For this reason, this cell-modified technique could be used for the treatment of liver-targeted diseases and/or disorders.

Genetic evidence for involvement of membrane trafficking in the action of 5-fluorouracil

To identify novel genes that mediate cellular sensitivity and resistance to 5-fluorouracil (5-FU), we performed a genome-wide genetic screening to identify altered susceptibility to 5-FU by Schizosaccharomyces pombe haploid nonessential gene deletion library containing 3004 deletion mutants. We identified 50 hypersensitive and 12 resistant mutants to this drug. Mutants sensitive or resistant to 5-FU were classified into various categories based on their putative functions. The largest group of the genes whose disruption renders cells altered susceptibility to 5-FU is involved in nucleic acid metabolism, but to our surprise, the second largest group is involved in membrane trafficking. In addition, several other membrane traffic mutants examined including gdi1-i11, ypt3-i5, Δryh1, Δric1, and Δaps1 exhibited hypersensitivity to 5-FU. Furthermore, we found that 5-FU in low concentration that generally do not affect cell growth altered the localization of Syb1, a secretory vesicle SNARE synaptobrevin which is cycled between the plasma membrane and the endocytic pathway. Notably, 5-FU at such low concentration also significantly inhibited the secretion of acid phosphatase. Altogether, our findings revealed the first evidence that 5-FU influences membrane trafficking as the potential underlying mechanism of the drug action.

Frequency of uridine monophosphate synthase Gly(213)Ala polymorphism in Caucasian gastrointestinal cancer patients and healthy subjects, investigated by means of new, rapid genotyping assays

AIMS

Uridine monophosphate synthase (UMPS) is a fundamental enzyme in pyrimidine synthesis. A single-nucleotide polymorphism, a G-C transversion at the 638th nucleotide, was demonstrated to increase UMPS activity and suggested to have clinical effects. The aims of this study were to set up simple genotyping methods and investigate the UMPS 638G>C polymorphism in the Caucasian population.

RESULTS

Two hundred forty-one patients with gastrointestinal cancers and 189 healthy subjects were enrolled. Genomic DNA was extracted from peripheral blood. A polymerase chain reaction-restriction fragment length polymorphism (RFLP) method was implemented using a forward primer incorporating a mismatched base to produce an artificial restriction site and BsrI restriction enzyme digestion; a denaturing high performance liquid chromatography (DHPLC) method was developed to further speed up UMPS genotyping. A 153 bp UMPS gene fragment was successfully amplified and analyzed in all samples. RFLP and DHPLC results showed a 100% match and where confirmed by direct sequencing. UMPS genotype distribution was similar in patients with cancer and control subjects.

CONCLUSIONS

Although no association was detected between UMPS variants and gastrointestinal cancer risk in Caucasians, polymerase chain reaction-RFLP with BsrI digestion and DHPLC set up at 59°C are reliable and cost-effective methods to genotype UMPS.

Adenovirus-mediated cytosine deaminase/5-fluorocytosine suicide gene therapy of human hepatoblastoma in vitro

BACKGROUND

Multidrug resistance is a key factor for the sobering outcome of relapsed and metastatic human hepatoblastoma (HB). Gene directed treatment approaches were recently identified as possible treatment options against advanced HB, in which standard chemotherapy regimens are partially insufficient. The aim of this study was to systematically analyze the effects of suicide gene therapy in three HB cell lines using a yeast-derived cytosine deaminase (YCD)-combined yeast uracil phosphoribosyltransferase (YUPRT)-based adenovirus-mediated gene transfer.

PROCEDURE

YCD and YUPRT were fused to form the bifunctional suicide gene SuperCD. Adeonoviral vectors were used for transduction. Tumor cells transduced at MOI 50 were incubated with 5-fluorocytosine (5-FC) in ascending concentrations.

RESULTS

Transduction rates were 87.8% (+6.7) in the mixed HB cell line HUH6, 98.6% (+1.4) in the epithelial HB cell line HepT1 and 93.6% (+0.6) in the multifocal HB embryonal cell line HepT3, respectively. In HepT3 and HepT1 cells suicide gene therapy with SuperCD/5-FC was highly effective leading to HB cell damage far above those of application of the prodrug 5-FC only. In HUH6 cells the approach had no effect due to a lack in activity of the CMV promoter being employed for transcription of the SuperCD transgene.

CONCLUSION

Assuming employment of fully active promoters, the SuperCD/5-FC approach may serve as a potentially useful anti-tumor strategy against advanced HB.

Specific targeting of prostate cancer cells in vitro by the suicide gene/prodrug system, uracil phosphoribosyltransferase/5-fluorouracil, under the control of prostate-specific membrane antigen promoter/enhancer

This study was designed to investigate the prostate cancer-specific tumoricidal effect of the suicide gene, Escherichia coli uracil phosphoribosyltransferase (UPRT), driven by the human prostate-specific membrane antigen promoter/enhancer (PSMA(E/P)) in vitro. When transfected with PSMA(E/P)-EGFP (enhanced green fluorescence protein) (a plasmid construct with the green fluorescence protein gene driven by the PSMA(E/P)), only the androgen-responsive and PSMA-positive prostate cancer cell line, LNCaP, expressed GFP, indicating the specificity of the PSMA(E/P) activity in androgen-sensitive and PSMA-positive prostate cancer cells. Taking advantage of this prostate cancer-specific property of PSMA(E/P), we successfully introduced bacterial UPRT into LNCaP cells where the tumoricidal effect of 5-fluorouracil (5-FU) was significantly increased when compared with the cells without the exogenous UPRT. We conclude that the efficacy of 5-FU-based chemotherapy in prostate cancers can be significantly improved by targeted expression of the suicide gene UPRT under the control of PSMA(E/P).

Identification and characterization of human uracil phosphoribosyltransferase (UPRTase)

Uracil phosphoribosyltransferase, which catalyzes the conversion of uracil and 5-phosphoribosyl-1-R-diphosphate to uridine monophosphate, is important in the pyrimidine salvage pathway and is an attractive target for rational drug design by incorporation of prodrugs that are lethal to many parasitic organisms specifically. So far, uracil phosphoribosyltransferase has been reported in Arabidopsis thaliana only, not in mammals. In this study, a novel uracil phosphoribosyltransferase family cDNA encoding a 309 amino acid protein with a putative uracil phosphoribosyltransferase domain was isolated from the human fetal brain library. It was named human UPRTase (uracil phosphoribosyltransferase). The ORF of human UPRTase gene was cloned into pQE30 and expressed in Escherichia coli M15. The protein was purified by Ni-NTA affinity chromatography, but UPRTase activity could not be detected by spectrophotometry. RT-PCR analysis showed that human UPRTase was strongly expressed in blood leukocytes, liver, spleen, and thymus, with lower levels of expression in the prostate, heart, brain, lung, and skeletal muscle. Subcellular location of UPRTase-EGFP fusion protein revealed that human UPRTase was distributed in the nucleus and cytoplasm of AD293 cells. Evolutional tree analyses of UPRTases or UPRTase-domain-containing proteins showed that UPRTase was conserved in organisms. UPRTases of archaebacteria or eubacterium had UPRTase activity whereas those higher than Caenorhabditis elegans, which lacked two amino acids in the uracil-binding region, had no UPRTase activity. This means that human UPRTase may have enzymatic activity with another, unknown, factor or have other activity in pyrimidine metabolism.

Combination of cytosine deaminase with uracil phosphoribosyl transferase leads to local and distant bystander effects against RM1 prostate cancer in mice

BACKGROUND

We aimed to evaluate the efficacy of gene-directed enzyme-prodrug therapy (GDEPT) using cytosine deaminase in combination with uracil phosphoribosyl transferase (CDUPRT) against intraprostatic mouse androgen-refractory prostate (RM1) tumors in immunocompetent mice. The product of the fusion gene, CDUPRT, converts the prodrug, 5-fluorocytosine (5FC), into 5-fluorouracil (5FU) and other cytotoxic metabolites that kill both CDUPRT-expressing and surrounding cells, via a 'bystander effect'.

METHODS

Stably transformed andogen-independent mouse prostate cancer (PC) cells, RM1-CDUPRT, -GFP or GFP/LacZ cells were used. To assess the local bystander effects of CDUPRT-GDEPT, immunocompetent C57BL/6 mice implanted with cell mixtures of RM1-GFP/CDUPRT and RM1-GFP cells in different proportions intraprostatically were treated with 5FC. Pseudo-metastases in the lungs were established by a tail vein injection of untransfected RM1 cells. At necropsy, prostate weight/volume and lung colony counts were assessed. Tumors, lymph nodes, spleens and lungs were frozen or fixed for immunohistochemistry.

RESULTS

CDUPRT expression in RM1-GFP/CDUPRT cells or tumors was confirmed by enzymic conversion of 5FC into 5FU, using HPLC. Treatment of mice bearing intraprostatic RM1-GFP/CDUPRT tumors with 5FC resulted in complete regression of the tumors. A 'local bystander effect' was seen, even though only 20% of the cells expressed CDUPRT. More importantly a significant reduction in pseudo-metastases of RM1 cells in lungs indicated a 'distant bystander effect'. Immunohistochemical evaluation of the treated tumors showed increased necrosis and apoptosis, with decreased tumor vascularity. There was also a significant increase in tumour-infiltration by macrophages, CD4+ T and natural killer cells.

CONCLUSIONS

We conclude that CDUPRT-GDEPT significantly suppressed the aggressive growth of RM1 prostate tumors and lung pseudo-metastases via immune mechanisms involving necrosis and apoptosis.

Combination of cytosine deaminase suicide gene expression with DR5 antibody treatment increases cancer cell cytotoxicity

Combined treatment using adenoviral-directed enzyme/prodrug therapy and immunotherapy has the potential to become a powerful alternative method of cancer therapy. We have developed adenoviral vectors encoding the cytosine deaminase gene (Ad-CD) and cytosine deaminase:uracil phosphoribosyltransferase fusion gene (Ad-CD:UPRT). A monoclonal antibody, TRA-8, specifically binds to death receptor 5, one of two death receptors bound by tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). The purpose of this study was to evaluate cytotoxicity in vitro and therapeutic efficacy in vivo of the combination of Ad-CD:UPRT and TRA-8 against human pancreatic cancer and glioma cell lines. The present study demonstrates that Ad-CD:UPRT infection resulted in increased 5-FC-mediated cell killing, compared with Ad-CD. Furthermore, a significant increase of cytotoxicity following Ad-CD:UPRT/5-FC and TRA-8 treatment of cancer cells in vitro was demonstrated. Animal studies showed significant inhibition of tumor growth of MIA PaCa-2 pancreatic and D54MG glioma xenografts by the combination of Ad-CD:UPRT/5-FC plus TRA-8 as compared with either agent alone or no treatment. The results suggest that the combination of Ad-CD:UPRT/5-FC with TRA-8 produces an additive cytotoxic effect in cancer cells in vitro and in vivo. These data indicate that combined treatment with enzyme/prodrug therapy and TRAIL immunotherapy provides a promising approach for cancer therapy.

Clinical role of orotate phosphoribosyl transferase and dihydropyrimidine dehydrogenase in colorectal cancer treated with postoperative fluoropyrimidine

BACKGROUND

Orotate phosphoribosyl transferase (OPRT) is an essential enzyme for activation of 5-fluorouracil (5-FU) and its derivatives. Dihydropyrimidine dehydrogenase (DPD) is a rate-limiting enzyme for degradation of 5-FU. In colorectal cancer (CRC), few studies have evaluated the relationship between OPRT, DPD, and clinicopathologic features.

METHODS

The study included 150 patients whose CRCs were classified into stage II to IV, and resected operatively. OPRT and DPD expression were evaluated using immunohistochemistry with new antibodies. Relationships between their expressions and clinicopathologic features. Survival curves were calculated using Kaplan-Meier method, and differences were evaluated with log-rank test. Cox proportional hazards model was also used.

RESULTS

OPRT expression showed a negative correlation with advances in venous invasion (P=.041), though DPD expression showed positive correlations with advances in venous invasion (P=.0053), and cancer stage (P=.0064). The patients survival rates were higher in those OPRT(+) than in those OPRT(-) (P=.004), and higher in those DPD(-) than in those DPD(+) (P=.008). The estimated hazard ratio for patients death with OPRT and DPD expression were 2.43 and 6.55 (P=.0047 and .0096) respectively.

CONCLUSIONS

OPRT expression was associated negatively with CRC progression and related with better prognosis, although DPD expression was positively correlated with CRC progression and related with poor prognosis. The overall patients survival rates were best in the patients OPRT(+)DPD(-), and worst in those OPRT(-)DPD(+) in treatment with fluoropyrimidine after operation.

Suicide gene therapy with an adenovirus expressing the fusion gene CD::UPRT in human glioblastomas: different sensitivities correlate with p53 status

BACKGROUND

Several gene therapy strategies have been designed for cancer treatment. Intra-tumoral injection of adenoviruses expressing pro-drug-converting enzymes is one such strategy. Although the efficacy of these therapies was tested in animal models, little work has been devoted to the determination of critical variables for success. In this work, we aimed at better understanding variables that affect the cytosine deaminase::uracil phosphoribosyl transferase (CD::UPRT)-based strategy in two human glioblastomas.

METHODS

We have constructed two adenoviruses expressing either CD or the fusion protein CD::UPRT. We have tested their anti-tumor activity in combination with 5-fluorocytosine (5-FC) in the glioblastoma cell lines U87 and U251, which are p53-wt and p53-deficient, respectively. Anti-tumor activity has also been investigated in spheroid structures.

RESULTS

The superiority of CD::UPRT over CD was confirmed in both glioblastoma cells. We found that the pro-drug concentration required for anti-tumor activity was 9-fold higher in U251 than in U87, while multiplicity of infection (MOI) as low as 6 was sufficient to achieve 50% killing. Bystander activity was observed with as few as 2 and 6% transduced cells for U87 and U251, respectively. Differences in sensitivity between U87 and U251 were not due to differences in transduction, transgene expression, or intercellular transport, but were related to 5-FU sensitivity and p53 status. Also, it is noteworthy that, in contrast to U87, U251 spheroids barely responded to the treatment, whereas their monolayer counterparts were very sensitive.

CONCLUSIONS

Our study has shown that p53 status is important for CD::UPRT/5-FC treatment. Moreover, this study demonstrated that the three-dimensional spheroid model is a more stringent in vitro model for suicide gene therapy evaluation than are monolayer cultures.

Effective Gene Therapy of Biliary Tract Cancers by a Conditionally Replicative Adenovirus Expressing Uracil Phosphoribosyltransferase: Significance of Timing of 5-Fluorouracil Administration

In order to enhance the efficacy of conditionally replicating adenoviruses (CRAd) in the treatment of cancers of the biliary tract, we studied the efficacy in vitro and in vivo of AxE1CAUP, a CRAd vector that carries a gene for uracil phosphoribosyltransferase (UPRT), which converts 5-fluorouracil (5-FU) directly to 5-fluorouridine monophosphate and greatly enhances the cytotoxicity of 5-FU. AxE1CAUP replicated and induced an increased UPRT expression in biliary cancer cells more efficiently than AxCAUP, a nonreplicative adenovirus carrying the UPRT gene. Whereas AxCAUP and AxE1AdB, a CRAd without the UPRT gene, modestly increased the sensitivity of BC cells to 5-FU, AxE1CAUP markedly increased the sensitivity, especially when the timing of 5-FU administration was appropriately chosen. AxE1CAUP replicated much less efficiently in normal WI-38 fibroblasts without any change in the sensitivity to 5-FU. In nude mice with s.c. biliary cancer xenografts, i.t. AxE1CAUP/5-FU therapy inhibited tumor growth significantly more strongly than AxCAUP/5-FU or AxE1AdB/5-FU therapy. Furthermore, in mice with peritoneally disseminated biliary cancer, i.p. AxE1CAUP efficiently proliferated in the tumors, decreased the tumor burden, and prolonged the survival of the mice when 5-FU was started 10 or 15 days after the vector inoculation, whereas earlier initiation of 5-FU resulted in early eradication of the vector and no survival benefit. The present study shows that the CRAd expressing UPRT was a more potent sensitizer of biliary cancer to 5-FU, than was a nonreplicative UPRT-encoding vector or a CRAd without UPRT gene, even at a lower dose of the vector, and that timing of 5-FU administration was a key factor to maximize the efficacy. This gene therapy with appropriately timed administration of 5-FU should be useful in overcoming the resistance of biliary cancers to 5-FU.

Potential therapeutic applications of recombinant, invasive E. coli

An invasive Escherichia coli expressing the inv gene from Yersinia pseudotuberculosis was used as a vector for protein delivery to mammalian epithelial cells. Upon incubation with beta1-integrin-expressing mammalian cells, the bacteria are internalized, allowing bacteria-encoded proteins to function from within the mammalian cell. These bacteria are eventually processed in the host phagosome where they are destroyed. Expression of listeriolysin O from Listeria monocytogenes in the bacterium and its subsequent release into the phagosome triggers the breakdown of the membrane, allowing the release of the bacterial content into the cytosol of host cells. Using this vector, we demonstrate delivery of a gene and intact, functional proteins into mammalian cells in which beta1-integrin is expressed and accessible. At a ratio of bacteria/mammalian cells compatible with the survival of the mammalian cells, protein delivery can be observed in the entire cell population in vitro, while gene transfer is far less efficient. Protein delivery can also be achieved in vivo in mouse tumour models and can be detected at least 96 h after inoculation. Functional, natural E. coli proteins are delivered in the process and can provide therapeutic benefit in vivo, when associated with prodrugs. This therapeutic effect is associated with infiltration of neutrophils, eosinophils, macrophages and to a lesser extent dendritic cells in the tumour mass.

Both gene expression for orotate phosphoribosyltransferase and its ratio to dihydropyrimidine dehydrogenase influence outcome following fluoropyrimidine-based chemotherapy for metastatic colorectal cancer

Activation of 5-fluorouracil into its nucleotides requires phosphorylation by three pathways involving orotate phosphoribosyl-transferase (OPRT), uridine phosphorylase (UP), or thymidine phosphorylase (TP). In this study, we investigated the association between gene expressions of these three enzymes and antitumour effect. Gene expressions in primary colorectal tumours were analysed by a real-time reverse transcriptional-polymerase chain reaction method in 37 patients receiving oral treatment of tegafur-uracil and leucovorin for metastatic diseases. The median values of OPRT mRNA expressions were 1.39 and 0.85 for responding tumours and nonresponding tumours, respectively, showing a statistically significant difference (P=0.0008). Responding tumours had statistically lower expressions of TP mRNA than nonresponding tumours (P=0.006). However, there was no difference in UP mRNA expression between responding and nonresponding tumours. Patients with high OPRT (>/=1.0) gene expression survived longer than those with low OPRT (<1.0) expression. Dihydropyrimidine dehydrogenase (DPD) gene expressions were measured. Responding tumours had a statistically higher OPRT/DPD ratio than the nonresponding ones (P=0.003). When the median value of the OPRT/DPD ratio was selected as the cutoff value, patients with a high OPRT/DPD ratio survived statistically longer than those with a low ratio (P=0.0014). In conclusion, both the expression of OPRT gene and the OPRT/DPD ratio might be useful as predictive parameters for the efficacy of fluoropyrimidine-based chemotherapy for metastatic colorectal cancer.

Improvement of carcinoembryonic antigen-specific prodrug gene therapy for experimental colon cancer

BACKGROUND

Improvement of tumor-specific gene expression is very important for achieving successful effects in prodrug gene therapy for advanced cancer with metastatic lesions. We used the Cre/loxP system for enhancing carcinoembryonic antigen (CEA)-specific prodrug gene therapy of cytosine (CD)/5-fluorocytosine (5-FC) for the treatment of a colon cancer model accompanied with liver metastases.

METHODS

Orthotopic colon cancer models were developed. Seven days later, adenovirus vector (3 x 10(9) pfu)was injected into the abdominal cavity, and 5-FC was administered for the next 10 days.

RESULTS

In these models, the double administration of AxCEANCre expressing Cre recombinase under the control of the CEA promoter, and AxCALNLCD expressing the CD gene under the control of the CAG promoter by the Cre-mediated switching system, completely inhibited liver metastases, and significantly reduced primary tumor volume compared to the administration of Mock or AxCEACD (P <.001). The survival periods of the mice treated with AxCEANCre and AxCALNLCD were longer than mice treated with Mock or AxCEACD, and longer than the mice treated with AxCACD (P <.05).

CONCLUSIONS

The enhanced CEA-specific prodrug gene therapy using the Cre/loxP system was useful for the treatment of advanced colon cancer with liver metastases, implicating clinical application.

Proteomic approach to understanding antibiotic action

We have used proteomic technology to elucidate the complex cellular responses of Bacillus subtilis to antimicrobial compounds belonging to classical and emerging antibiotic classes. We established on two-dimensional gels a comprehensive database of cytoplasmic proteins with pIs covering a range of 4 to 7 that were synthesized during treatment with antibiotics or agents known to cause generalized cell damage. Although each antibiotic showed an individual protein expression profile, overlaps in the expression of marker proteins reflected similarities in molecular drug mechanisms, suggesting that novel compounds with unknown mechanisms of action may be classified. Indeed, one such substance, a structurally novel protein synthesis inhibitor (BAY 50-2369), could be classified as a peptidyltransferase inhibitor. These results suggest that this technique gives new insights into the bacterial response toward classical antibiotics and hints at modes of action of novel compounds. Such a method should prove useful in the process of antibiotic drug discovery.

Gene therapy for prostate cancer using the cytosine deaminase/uracil phosphoribosyltransferase suicide system

BACKGROUND

Cytosine deaminase (CD) activates prodrug 5-FC to 5-FU and is used for suicide gene therapy (the CD/5-FC system). E. coli uracil phosphoribosyltransferase (UPRT) is a pyrimidine salvage enzyme that directly converts 5-FU into 5-fluorouridine monophosphate and improves the antitumoral effect of 5-FU. This study demonstrates the effectiveness of transduction of the UPRT gene in addition to CD/5-FC cancer suicide gene therapy.

METHODS

We investigated a combined suicide gene transduction therapy for human hormone independent prostate cancer cell line DU145 using two separate adenovirus vectors expressing the E. coli CD and E. coli UPRT genes and systemic 5-FC administration (the CD+UPRT/5-FC system).

RESULTS

Cells transfected with AdCA-UPRT showed approximately 57 times lower IC50 to 5-FU compared with those transfected with AdCA-LacZ. Furthermore, cells transfected with AdCA-CD and AdCA-UPRT proved to be more sensitive to 5-FC compared with those transfected with AdCA-CD. Intratumoral injection of AdCA-CD and AdCA-UPRT drastically suppressed the growth of tumors which had generated from DU145 cells inoculated into athymic (nude) mice compared with those injected with AdCA-LacZ or AdCA-LacZ and AdCA-CD.

CONCLUSIONS

These results suggest that the CD+UPRT/5-FC system could be a powerful factor in human prostate cancer suicide gene therapy.

P53 overexpression predicts poor chemosensitivity to high-dose 5-fluorouracil plus leucovorin chemotherapy for stage IV colorectal cancers after palliative bowel resection

Our study aims to further clarify the prognostic significance of p53 overexpression in stage IV colorectal cancer. Between January 1994 and June 1997, we recruited 144 patients with stage IV colorectal cancers for our study, based on appropriate eligibility criteria. The patients were nonrandomly allocated to 2 treatment groups of either with or without high-dose 5-fluorouracil plus leucovorin chemotherapy (HDFL: 5-Fu: 2,600 mg/m(2) leucovorin 300 mg/m maximum 500 mg). Each treatment group was further divided into 2 subgroups according to the status of p53 overexpression. Therefore, 4 subgroups were allocated in our study and were designated as p53 (overexpression) HDFL (+), n = 65; p53 (normal) HDFL (+), n = 37; p53 (overexpression) HDFL (-), n = 27; and p53 (normal) HDFL (-), n = 15, respectively. All patients were prospectively followed until April 2001. There was no significant difference of the background clinicopathologic data of these 4 allocated subgroups of patients (p > 0.05). Multivariate analysis of various clinicopathologic factors of the whole group of patients indicated that age > or = 60 years, poor differentiation, mucin production, CEA > 100 ng/ml, p53 overexpression and without chemotherapy were the significant independent poor prognostic factors (p < 0.05). Survival analyses indicated that the patients of subgroup p53 (normal) HDFL (+) survived significantly longer than those of subgroup p53 (overexpression) HDFL (+), with mean survival time (95% confidence interval [CI]) of 20.24 (16.24-24.25) and 13.29 (10.98-15.60) months, respectively (p = 0.0043, log-rank test). In contrast, in patients without chemotherapy, the prognosis was poor regardless of their p53 status, with mean survival time (95% CI) of 6.85 (5.47-8.23) and 5.87 (4.48-7.26) months in p53 (overexpression) HDFL (-) and p53 (normal) HDFL (-) subgroups of patients, respectively (p = 0.2820, log-rank test). Cancers of normal p53 expression responded significantly better to HDFL (p < 0.05), with mean response rate (95% CI) being 65.57% (52.18-82.96%) in subgroup p53 (normal) HDFL (+) as compared to 35.38% (23.52-47.24%) in subgroup p53 (overexpression) HDFL (+). The toxicity to HDFL was similarly minimal between p53-normal and p53-overexpression patients (p > 0.05). We thus concluded that the poorer prognosis of stage IV colorectal cancers with p53 overexpression was associated with their poorer chemosensitivity rather than the more biologic aggressiveness.